1. Field of the Invention
This invention relates to a polymerizable composition useful for making crosslinked copolymers of vinylpyrrolidone and vinyl caprolactam, and, more particularly, to a process for making such crosslinked copolymer by proliferous polymerization in the absence of base.
2. Description of the Prior Art
Crosslinked polyvinylpyrrolidone (PVP) is made by popcorn or proliferous polymerization of vinylpyrrolidone (VP), in the absence or presence of crosslinking agents, as described in U.S. Pat. Nos. 3,277,066; 3,306,886; 3,759,880; 3,933,766; and 3,992,562; and by F. Haaf et al. in Polymer J. 17(1), p. 143-152 (1985), in an article entitled, "Polymers of N-Vinylpyrrolidone: Synthesis, Characterization and Uses". Polymerization of vinylpyrrolidone can occur in the absence of added crosslinker because the requisite crosslinker in the process is formed in situ during the first stage heating of vinylpyrrolidone in aqueous caustic solutions at temperatures&gt;100.degree. C., e.g. at 140.degree. C. These in situ crosslinkers have been identified by gas chromatography and other analytical techniques as 1-vinyl-3-ethylidene pyrrolidone and ethylidene-bis-3-(N-vinylpyrrolidone). These compounds also are believed to be present in very small amounts in reaction mixtures which had been cooled to room temperature. However, after the polymerization was completed, these bifunctional compounds could not be found in the final polymer product. Accordingly, the named bifunctional monomers have been considered to be present only in small amounts during the polymerization and consumed in the process of forming the crosslinked PVP polymer.
Tseng, S. and Wolf, P. in U.S. Pat. Nos. 5,274,120; 5,286,876; 5,360,883; 5,342,964; 5,391,668; and 5,393,854, described the preparation of the isomeric compound 1-vinyl-3(E)-ethylidene pyrrolidone (EVP) in a purity of at least 95%, in the form of white, needle-shaped crystals having a melting point of 59.degree.-61.degree. C., and a polymerizable composition including EVP as crosslinker for making crosslinked polyvinylpyrrolidone rapidly upon heating the composition at about 80.degree.-120.degree. C. in the absence of base.
Crosslinked polymers of vinyl pyrrolidone have been used extensively to purify beer and wine solutions. However, it is desired to provide new and improved polymers for use in this industry, particularly for filtering out polyphenols in beer which give it a stale taste.
Accordingly, it is an object of this invention to provide a polymerizable composition of about 50 to about 90% by weight of vinyl pyrrolidone monomer, about 10 to about 50% by weight of vinyl caprolactam monomer, and about 0.5 to about 7% by weight of a crosslinker, which is capable of proliferous polymerization in the absence of base at about 80.degree. to about 120.degree. C.
Another object is to provide a process for making crosslinked copolymers of vinyl pyrrolidone and vinyl caprolactam by (a) providing the polymerizable composition described above, preferably including water, and (b) heating said composition in the absence of base at about 80.degree. to about 120.degree. C. for about 1 to about 10 hours, under vigorous agitation, in an inert atmosphere.
Still another object is to provide a crosslinked copolymer product of vinyl pyrrolidone and vinyl caprolactam.
These and other objects and features of the invention will be made apparent from the following description of the invention.